With the exhaustion of the world's power resources, the necessity to utilize low-grade solid fuels becomes more and more urgent. Most efficient use of such fuels can be achieved after the same have been converted through heat processing into high-calorific solid and liquid products. Capital and operating expenses and power consumption in processing low-grade fuels are at present rather high. In this connection there is an urgent need to raise the yield of high-quality products produced by heat processing of solid fuels without increasing said expenses. Thus, methods based on slow heating of pulverized fuels being processed were at one time replaced by methods of heat processing of solid fuels involving heating such fuels in less than 1 second to a temperature of their intensive thermal decomposition. Such methods of rapid heating of fuel bring about an increased yield of both solid and liquid products. However, these methods have a disadvantage residing in overheating small particles of the fuel being pyrolyzed, which is caused by a great difference in the temperature between the gaseous heat carrier and the coal being processed. It is known that overheating of the coal particles results in a decreased yield of useful vapour and gas products. In addition, the consumption of the gaseous heat carrier for heating and pyrolysis of brown coal is rather high, and the efficiency of the process is further reduced through the non-utilization of the physical heat of the gas and vapour mixture exiting from the fuel pyrolysis chamber.
A method of and apparatus for heating processing of pulverized brown coal are disclosed in USSR Inventor's Certificate No. 372.244. Said method includes the following steps: a first stage of heating brown coal by a gaseous heat carrier in less than 1 second to a temperature of 500.degree.-800.degree. C., at which terminal decomposition of the brown coal takes place with the formation of a vapour and gas suspension comprising solid pulverized matter and a vapour and gas mixture, the resultant vapour and gas mixture being removed to be purified and condensed to produce gas and liquid products; a second stage of heating of the brown coal in the form of solid matter by a gaseous heat carrier to a temperature of 600.degree.-900.degree. C. at which complete thermal decomposition of the brown coal takes place with the formation of a vapour and gas mixture and a solid pulverized product, the resultant vapour and gas mixture being delivered back to the first stage of heating, which permits utilizing the heat carrier, already used at the second stage of heating, for preheating the brown coal particles without their being overheated. The brown coal to be processed is preheated by a gaseous heat carrier to a temperature of 200.degree.-300.degree. C. prior to its being fed into the chamber for the first-stage heating.
Said apparatus for heat processing pulverized brown coal comprises a chamber of the first-stage heating of the brown coal, said chamber being provided with a means for feeding brown coal therein, a means for feeding a gaseous heat carrier therein and a means for removing therefrom a vapour and gas mixture resulting from the thermal decomposition of the brown coal, a chamber for the second-stage heating of the brown coal to a temperature of complete thermal decomposition thereof, which chamber is successively connected with the chamber for the first-stage heating and is provided with a means for feeding therein a gaseous heat carrier, the chamber for the second-stage heating being connected to the chamber for the first-stage heating by a return conduit for feeding the vapour and gas mixture. In addition, the apparatus incorporates a chamber for preheating the brown coal to a temperature of 200.degree.-300.degree. C. This chamber is arranged before the chamber for the first-stage heating and is successively connected therewith. There is also a chamber for the additional withdrawal of gas which communicates in series with the chamber for the second-stage heating.
Attempts have been made to solve the problem of keeping the small fuel particles, particularly, of brown coal, from overheating and of reducing the heat carrier consumption in the carrying out of the above method and the use of the apparatus. Experience has shown, however, that this is unattainable, since the vapour and gas mixture which is delivered back to the first stage of heating of brown coal, and which is substantially a gaseous heat carrier, cannot provide uniform heating of both large and small particles. When small particles are normally heated, the large ones are heated insufficiently, which does not ensure complete thermal decomposition thereof, and, hence, reduces the yield of gaseous and liquid products. To achieve complete thermal decomposition of large particles, one must raise the temperature of heating of the whole batch of brown coal being processed in the first stage. In this case the overheating of small particles and, hence, increased consumption of the gaseous heat carrier are inevitable. Moreover, an increased proportion of the gaseous heat carrier in the vapour and gas mixture results in worsening of the quality of the resultant gaseous products.
It is an object of the invention to overcome the above disadvantages.
Another object of the invention is the provision of a method of and an apparatus for heat processing of pulverized brown coal which ensure an increased yield of vapour and gas products.
Still another object of the invention is to provide a method of and an apparatus for heat processing of pulverized brown coal which ensure an increased yield of vapour and gas products with the same power consumption as in the prior art method and apparatus for heat processing of pulverized brown coal.
It is a further object of the invention to provide a method of and an apparatus for heat processing of pulverized brown coal which yield gaseous products of a higher quality.